John Asher Johnson

Exploring the Relationship Between Stellar Mass and Planet Occurrence
Contact information:
Institute for Astronomy
2680 Woodlawn Dr.
Fellowship status:
Starting year: 2007
AAPF alumnus
Fellowship institution: University of Hawaii Institute for Astronomy
Current (or last known) position: Professor of Astronomy, Harvard University
Research Interests:

A planet--bearing star can be thought of as a very bright, extremely dense remnant of a protoplanetary disk. After all, a star inherits its defining characteristics---its mass and chemical composition---from the same disk material that forms its planets. The physical characteristics of planet host stars therefore provide a crucial link between the planets we detect today and the circumstellar environments from which they formed long ago. Studying the relationships between the observed occurrence rate and orbital properties of planets as a function of stellar characteristics informs theories of planet formation, and also helps guide the target selection of future planet searches.

I am conducting a search for planets around a sample of 240 intermediate-mass subgiant stars at the Keck Observatory. Compared to their A- and F-type main-sequence progenitors, these evolved stars are ideal planet search targets, owing to their low rotation rates, low surface temperatures and stable atmospheres. The planets detected from this sample of stars will allow me to study the effect of stellar mass on giant planet formation and planetary system architecture.

My other interests include:

  • Precision photometric follow-up of transiting exoplanets
  • Modeling the Rossiter-McLaughlin effect for transiting planets to measure the spin-orbit alignment of exoplanetary systems.
  • Searching for planets around M Dwarfs as a member of the California and Carnegie Planet Search
  • Searching for planets around metal-rich stars as a member of the Next 2000 Stars Consotium (N2K)
  • Variable Pre-main-sequence stars named KH15D
Education and Outreach Interests:

Exoplanets provide an exciting launching point for teaching young students about astronomy. The PI will implement a program of educational outreach in elementary schools using hands-on and multimedia activities that merge planetary science and state-mandated science standards. The lesson plans will be taught in collaboration with Honolulu-area 4th and 5th grade teachers. The activities are designed to take students on a journey that begins at the Sun, progresses through the planets of our Solar System, and culminates with the exotic worlds recently discovered around other stars. By serving as a minority role model, the PI is uniquely positioned to encourage young, underrepresented students to pursue careers in astronomy.